This disclosure is directed to a sensor for converting certain measurements into a signal suitable for laser transmission, and further sets forth a laser which appropriately encodes the sensed variable, transmits the encoded variable, and enables the transmitted signal to be received. It is particularly adapted for use in systems involving high impact e.g., in using a steam powered pile driver or hammer to drive a piling. In this particular example, a piling of any length and substantial size is subjected to severe impact or shock loading. In a typical situation, assume that a steam powered hammer is positioned to drive a long pile through a pile jacket into the mud bottom beneath a body of water with mud of any depth and water of typical depth. The piling is subjected to severe impact or shock loading which can peak at many g's. With each stroke of the hammer, the hammer falls at instantaneous high velocity, delivers impact to the piling. Several variables are important. One variable is the rate of movement of the gauge position on the piling. Another important factor may be the velocity of the hammer that strikes the piling. There is some energy loss between hammer and piling so that the motion of the hammer and motion of the piling are different. Another important factor is the stress wave which propagates along the piling. This normally has the form of strain which can be observed in the piling.
In the latter instance, the strain is typically measured by a strain gauge on the piling. The present invention enables strain gauge measurements to be obtained away from the piling through wireless communication. More specifically, the present apparatus utilizes a laser telemetry system to encode by means of the laser any data of interest in the laser signal. This arrangement conveys the strain or other data to a remote location where a receiver can be located, thereby enabling the strain or other information to be received, amplified, demodulated as appropriate and converted into data for subsequent analysis and processing.
The strain gauge function is accomplished by means of changing the length of the laser resulting in a change of frequency output of the laser. One application of this concept is to an apparatus comprised of an injection laser diode (ILD). It is supported on a substrate. The substrate is affixed to the piling. The substrate is then subjected to the strain of the piling and thereby applies strain to the ILD. The strain of the laser cavity, a change in length per unit length, causes a shift in the lasing frequency. The unstrained laser has a nominal lasing frequency. As strain occurs, the lasing frequency shifts to thereby encode the strain in the frequency. The strain in the piling is directly proportional to the change in frequency divided by the nominal frequency. This variable is transmitted as a function of frequency and hence is an FM system where the strain is encoded in frequency change, not amplitude. The shift in frequency is discerned from the laser beam. A receiver located remote from the laser transducer picks up the beam for data retrieval.
In addition to this, the laser can be used to determine movement of the piling to which it is attached. It also can be used to measure hammer velocity. One lob in the field pattern transmitted from the laser can be used to measure the distance from the laser to the remote receiver to thereby provide an indication of movement of the laser position on the piling. The particle velocity in the piling, with respect to the position of the remote receiver, is then determined by means of a Doppler effect. A different lob in the field pattern transmitted from the laser can be used so that hammer velocity is determined by means of a Doppler effect. To this end, the laser transmits the signal to a reflector mounted on the hammer which is reflected to a receiving system, encoding hammer velocity in a Doppler shift.
Another important application of the present apparatus is in the measurement of stresses and vibration occurring in rotating machinery. A typical rotating machine might be a motor, generator, compressor or turbine. Another type machine might be a centrifugal pump. In this context, a machine typically has an external fixed cabinet or housing which encloses the rotating parts. The rotating parts are subjected to stress and vibration. Heretofore, it has been possible to obtain such data and send it out of the machine either by means of commutated conductors or perhaps through an FM telemetry system. The present apparatus however overcomes the limitations of such apparatus and provides a system combining the sensor with the telemetry linking equipment. The sensor is preferably a laser which responds by forming modulated laser output data and is thereby able to transmit free of commutator for reception adjacent to the rotating machinery. For instance, assume that the rotating machinery is susceptible of significant damage and harm in the event that the bearings of the shaft of the rotating machinery were to fail. Partial bearing failure is typically indicated by vibrations coupled through the shaft to the rotating components of the machinery. Other variables of interest can be coupled through the laser for reception remote from the rotating components free of commutated connection.
As will be understood, the foregoing describes different settings in which the apparatus of the present disclosure can be installed and used to provide data indicative of strain, vibration, movement or velocity. It takes advantage of the sensitivity of a laser to the direct mounting of the laser on the equipment to be monitored and therefore is able to convert the monitored data into a laser beam modulation and therefore is successful in delivery of the variable of interest without commutation. A quality linkage is achieved free of the difficulties and maintenance associated with commutators, FM telemetry systems, and the like.